Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Loans Held For Sale | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 495	$ 832
Aggregate Unpaid Principal Balance - Assets	478	807
Difference - Assets	17	25
Loans Held For Sale | Commercial Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	396	830
Aggregate Unpaid Principal Balance - Assets	411	845
Difference - Assets	(15)	(15)
Loans Held For Sale | Performing Loans | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	489	822
Aggregate Unpaid Principal Balance - Assets	472	796
Difference - Assets	17	26
Loans Held For Sale | Performing Loans | Commercial Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	396	828
Aggregate Unpaid Principal Balance - Assets	411	842
Difference - Assets	(15)	(14)
Loans Held For Sale | Accruing loans 90 days or more past due | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	2	3
Aggregate Unpaid Principal Balance - Assets	2	3
Loans Held For Sale | Nonaccrual Loans | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	4	7
Aggregate Unpaid Principal Balance - Assets	4	8
Difference - Assets		(1)
Loans Held For Sale | Nonaccrual Loans | Commercial Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets		2
Aggregate Unpaid Principal Balance - Assets		3
Difference - Assets		(1)
Loans | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	782	869
Aggregate Unpaid Principal Balance - Assets	919	1,028
Difference - Assets	(137)	(159)
Loans | Performing Loans | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	279	251
Aggregate Unpaid Principal Balance - Assets	298	280
Difference - Assets	(19)	(29)
Loans | Accruing loans 90 days or more past due | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	321	421
Aggregate Unpaid Principal Balance - Assets	329	431
Difference - Assets	(8)	(10)
Loans | Nonaccrual Loans | Residential Mortgage
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	182	197
Aggregate Unpaid Principal Balance - Assets	292	317
Difference - Assets	(110)	(120)
Other Assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	156	216
Aggregate Unpaid Principal Balance - Assets	176	212
Difference - Assets	(20)	4
Other borrowed funds
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	64	84
Aggregate Unpaid Principal Balance - Liabilities	65	85
Difference - Liabilities	$ (1)	$ (1)